svp aidez moi urgent svp

bonjour,

1a) (1000-3)(1000+3)=
1000*1000 + 1000*3 - 1000*3 -3*3 =
100000-9 = 999 991

997*1003 =
(1000-3)(1000+3) = tu finis

b) 491*509 = (500-9)(500+9) = tu developpes, tu réduis

2) figure 1 : (a+b)(a-b) = a²-b²
    figure 2 : a(a-b)+b(a-b) = a²-ab+ab-b² = a²-b²
    figure 3 : a(a-b)+b(a-b) = a²-ab+a²-b² = a²-b²

3) ( a-b)(a+b) = a²+ab-ab-b² = a²-b²